1. Field of the Invention
The invention relates to a coated sliding element, such as a piston ring, and methods of manufacturing the coated sliding element.
2. Related Art
Sliding elements of engine applications typically consist of multiple-layer materials with modified surfaces to optimize the sliding characteristics. For example, the sliding elements can include metal layers, possibly based on lead, tin or aluminum, which are applied by a galvanic process, vaporization, or ion plating. Non-metal sliding layers are also known, such as those having an artificial resin base modified to achieve certain properties, load capacity, and resistance to wear.
Although the load capacity provided by the known coatings is high, failure of the sliding function can result if the load capacity limit is exceeded. The associated exposure of the substrate material can then cause seizure leading to total failure of the sliding element.
Resin-based sliding coatings have also been used for many years to reduce friction in mechanical constructions. Usually, metal, plastic and rubber components are coated, which need to be easily movable without further lubrication. In typical applications, the loads are rather low and the boundary conditions, such as temperature and media, are non-critical. It is known from various publications, in particular from EP 0 984 182 A1, that engine applications, for example crank shaft bearings, are also possible with such sliding elements. In this document, an overlay with a matrix of polyimide (PI), polyamideimide (PAI), epoxy resin or a phenolic resin is described, to which Fe3O4 can be added, amongst others, to reduce wear.
DE 196 14 105 A1 reveals a wear and cavitation-resistant plastics sliding layer consisting of a matrix material made of polytetrafluoroethylene (PTFE) or thermoplastic fluoropolymers, Fe2O3, and solid lubricants. This material is used for bearings, for example as a guide element for shock absorbers, and is only suitable for low sliding speeds and low loads due to its structure and the soft fluoropolymer matrix.
EP 1 775 487 A2 discloses a sliding bearing which has a metal carrier material, and an aluminum alloy and plastic sliding layer applied to the metal carrier material. In order to improve the bonding strength and cavitation resistance of the plastic sliding layer, a material is suggested that has a bonding agent made of PI, PAI, polyben-zimidazole (PBI), engineered (EP), and functional polymer (FP), as well as a solid lubricant such as MoS2, graphite, PTFE, and BN.